AI-centered US stock bull market nears four-year anniversary

• The S&P 500 has gained 117% since October 2022, ranking as the sixth-best performing bull market since World War Two and eighth-longest in duration
• AI spending drives approximately one-third of recent US economic growth, with S&P 500 earnings expected to rise over 35% this year; Nvidia's market cap has soared from $286 billion to $5.8 trillion
• Market concentration risk has intensified as the top 10 S&P 500 companies now represent about 40% of the index (up from 28% in 2022), while the 10-year Treasury yield near 5.2% creates increased competition for equity investments

Summary: AI-Centered US Stock Bull Market Nears Four-Year Anniversary

The US bull market approaches its four-year milestone on October 12, 2025, with the S&P 500 trading near record highs after more than doubling—up 117%—since its October 2022 cycle low. This performance ranks as the sixth-best bull market since World War II and the eighth-longest.

Key Drivers:

Artificial Intelligence has been the dominant force, with ChatGPT launching just one month after the bull market began. S&P 500 earnings are expected to rise over 35% this year, driven by hyperscaler capital spending on AI data centers. Oxford Economics estimates AI contributes approximately one-third of recent US economic growth through direct infrastructure investment and wealth-effect-driven consumer spending.

Sector Performance:

Only technology and communication services sectors have outperformed the broader index during this period. Nvidia exemplifies the AI boom, with its market capitalization surging from $286 billion to $5.8 trillion, making it the world's largest company. Thirteen US companies now exceed $1 trillion in market value, nearly all with significant tech or AI exposure.

Key Risks:

• Concentration: The top 10 S&P 500 companies now represent 40% of the index, up from 28% in October 2022, creating vulnerability if AI momentum falters
• Federal Reserve Policy: Recent rate hikes aimed at combating inflation could slow economic growth
• Rising Bond Yields: The 10-year Treasury yield hovers around 5.2%, its highest in 24 years, making bonds more competitive with equities

Analysts warn that while bull markets don't die of old age, the "easy money" in AI may have been made, requiring companies to demonstrate that massive AI spending translates into actual profits.